Method and apparatus for spray fractionation of particles in liquid suspension

Abstract

Fractionation apparatus (20) is disclosed which utilizes a rapidily rotating disk which receives a liquid suspension of particles to be separated onto its rotating face surface (35). When the film of liquid and particles on the rotating face surface (35) reaches the peripheral edge (38) of the face, particles above a certain size are radially ejected while smaller particles and the liquid are carried over the edge onto the surface of a depending rim (39). The suspension of smaller particles and liquid is carried down the rim to the rim edge (40) at which point the smaller particles and liquid are disengaged. A separator wall (27) may be interposed between the two streams of particles emanating from the disk (24) to provide a physical separation of the larger and smaller particles once they have left the disk. The characteristics of the face surface, the angle of the rim with respect to the face, the disk speed, suspension feed rate, and other operating conditions can be selected such that highly efficient fractionations of particle suspensions, such as wood pulp slurries, can be obtained about a selected break point particle size.

What is claimed is: 
     
       1. Apparatus for fractionating a mixture of particle of different sizes suspended in a liquid to produce at least two portions of particles separated by size, comprising: (a) a disk symmetrical about an axis, having a face surface terminating in a sharp, circular edge, a rim extending away from the face edge such that at the face edge a plane tangent to the surface of the rim intersects a plane tangent to the surface of the face at an angle of about 20° or more, and the rim intersects a plane perpendicular to the axis of symmetry of the disk at an angle of 90° or less, the rim terminating in a rim edge with the length of the rim between the face edge and the rim edge being sufficient to allow a suspension of particles and liquid to turn over the face edge and form a film on the rim, the face and rim surfaces being adapted to allow a stable film of the liquid carrying the particles to form thereon;   (b) means for rotating the disk about its axis of symmetry;   (c) a supply outlet mounted such that a mixture of particles in suspension in a liquid can be supplied therethrough onto the disk face; and   (d) a separator wall mounted to separate material ejected in a first stream radially outward from the face edge of the disk from material ejected in a second stream from the rim of the disk, the separator wall having an inner edge closely adjacent to the rim of the disk and at a position intermediate the face edge and the rim edge to thereby physically separate the first and second streams so that they do not substantially mix.   
     
     
       2. The apparatus of claim 1 including enclosure walls surrounding the disk and the separator wall and wherein the separator wall defines, with the enclosure walls, two chambers, one chamber collecting material discharged radially outward from the face edge of the disk in the first stream and the other chamber collecting material discharged in the first stream at an angle to a horizontal plane perpendicular to the axis of symmetry of the disk. 
     
     
       3. The apparatus of claim 1 wherein the face surface of the disk is flat and horizontal and the rim extends downwardly from the face. 
     
     
       4. The apparatus of claim 1 wherein the face surface is flat and horizontal and the rim extends upwardly from the face. 
     
     
       5. The apparatus of claim 1 wherein the surface of the rim of the disk has the shape of a frustum of a cone and intersects a plane perpendicular to the axis of symmetry of the disk at an angle between approximately 22° and 68°. 
     
     
       6. The apparatus of claim 1 or 5 wherein the face surface is flat and the length of the rim between the face edge and the rim edge is at least 3/8 inch. 
     
     
       7. The apparatus of claim 6 wherein the face of the disk is approximately 6 inches in diameter. 
     
     
       8. The apparatus of claim 1 wherein the length of the rim between the face edge and the rim edge is about 2 inches. 
     
     
       9. The apparatus of claim 1 wherein the face surface is convex. 
     
     
       10. The apparatus of claim 1 wherein the face surface is concave. 
     
     
       11. The apparatus of claim 1 wherein the means for rotating the disk is attached to the side of the disk opposite the disk face. 
     
     
       12. Apparatus for fractionating a mixture of particles of different sizes suspended in a liquid to produce at least two portions of particles separated according to size, comprising: (a) a disk symmetrical about an axis of symmetry, the disk having a flat face which is smooth and wettable, a sharp, circular edge bounding the face, and a smooth, wettable rim extending away from the face edge and terminating at a rim edge, the rim intersecting the plane of the face at an angle between 90° and 5°;   (b) means for rotating the disk about its axis of symmtry;   (c) a supply outlet mounted such that a mixture of particles in suspension in a liquid can be supplied therethrough onto the disk face;   (d) a collector having at least two compartments positioned to collect spray from the disk at two separate elevations with respect to the disk, one collector compartment positioned to receive the portion of the spray containing course materials above a selected size, and the other compartment positioned to receive the portion of the spray containing the major portion of the liquid carrier and the fine particles smaller than the selected size.   
     
     
       13. The apparatus of claim 12 including enclosure walls around the disk to confine all of the spray from the disk. 
     
     
       14. The apparatus of claim 12 wherein the disk has a rim at least 3/8 inch long which extends downwardly from the face edge of the disk at an angle with respect to the face surface of 90°. 
     
     
       15. The apparatus of claim 12 wherein the disk has a rim at least 3/8 inch long formed in the shape of a frustum of a cone with the surface of the rim intersecting the plane of the face surface at an angle between approximately 22° and 68°. 
     
     
       16. The apparatus of claim 12 wherein the disk has a rim having the shape of a frustum of a cone which extends downwardly from the face edge and has a length between the face edge and the rim edge of at least 2 inches and less than 4 inches and which forms an angle with respect to the plane of the face surface between approximately 22° and 68°. 
     
     
       17. The apparatus of claim 15 or 16 wherein the diameter of the face surface is approximately 6 inches. 
     
     
       18. The apparatus of claim 12 wherein the means for rotating the disk is attached to the side of the disk opposite the disk face. 
     
     
       19. The apparatus of claim 18 wherein the means for rotating the disk includes an electrical drive motor having a drive shaft extending therefrom and attached to the side of the disk opposite the face to support the disk for rotation. 
     
     
       20. The apparatus of claim 12 wherein the compartments of the collector are separated by a separator plate having an inner edge which is mounted adjacent to the rim of the disk intermediate the face edge and the rim edge. 
     
     
       21. The apparatus of claim 12 wherein the collector includes a plurality of compartments mounted in ascending vertical arrangement to collect the spray from the rotating disk at a plurality of heights, including a position directly radially outward from the face edge of the rotating disk and a position directly radially outward from the rim edge of the disk. 
     
     
       22. A method of separating particles by size from a mixture of particles of various diameters which are suspended in a liquid, comprising the steps of: (a) rotating a disk about its axis of symmetry, the disk having a face surface terminating in a sharp peripheral face edge and a rim at least 3/8 inch long extending away from the face edge and terminating in a rim edge, the rim surface intersecting a plane perpendicular to the axis of rotation of the disk at an angle between approximately 5° and 90°;   (b) supplying a suspension of particles in liquid to the face of the disk, the suspension containing a mixture of particles having diameters less than and greater than a selected break point diameter;   (c) selecting the speed of rotation of the disk to be sufficient to result in particles having a diameter greater than the break point diameter being ejected from the disk at the face edge while particles below the break point diameter are carried with the liquid over the face edge and onto the rim, and selecting the rate of flow of the liquid suspension to the face such that a stable film of the liquid suspension is formed on the face surface and rim surface; and   (d) collecting the material that is discharged directly radially outward from the face edge and separately collecting the material that is discharged outwardly from the rim of the disk.   
     
     
       23. The method of claim 22 wherein the suspension of particles in liquid supplied to the disk is a suspension of fibers in water, the fibers comprising a mixture of fibers of different diameters, the speed of rotation of the disk and the rate of flow of the suspension being selected to provide separation of the fibers about a chosen fiber diameter. 
     
     
       24. A method of separating particles of differing sizes which are contained in a liquid carrier, comprising the steps of: (a) rotating a disk about a vertical axis, the disk having a flat face surface, a sharp, circular peripheral face edge defining the boundary of the face surface, and a rim extending away from the face edge at an angle between approximately 90° and 20° with respect to the plane of the face surface and terminating in a rim edge;   (b) supplying a mixture of particles of differing sizes in a liquid carrier to the face of the rotating disk;   (c) collecting the spray from the rotating disk which is impelled substantially radially from the face edge, such portion of the spray containing primarily course particles above a size selected for separation; and   (d) collecting the spray impelled outwardly from the rim and which is separated by a vertical distance from the portion of the spray which is directed radially from the face edge, such portion of the spray containing primarily the liquid carrier and the fine particles which are below the size selected for separation.   
     
     
       25. The method of claim 24 wherein the particles are fibers of differing diameters suspended in water. 
     
     
       26. Apparatus adapted for use in separating particles in liquid suspension by size, comprising: (a) a disk symmetrical about an axis of symmetry, the disk having a flat face on one side which is smooth and wettable, a sharp, circular edge bounding the face, and a smooth, wettable rim extending away from the face edge and terminating at a rim edge, the length of the rim from face edge to rim edge being at least 3/8 inch and the rim interecting the plane of the face at an angle between 90° and 5°; and   (b) means attached to the disk on the side thereof opposite to the face for rotating the disk about its axis of symmetry.   
     
     
       27. The apparatus of claim 26 wherein the rim intersects the face at an angle between approximately 22° and 68°. 
     
     
       28. The apparatus of claim 27 wherein the rim is between about two to four inches long.